Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

dēmensum, i, n., v. demetior.

dēmensus, a, um, Part. demetior.

dē-mētĭor, mensus, 4, v. a., to measure out, to measure, as a whole (whereas dimetior is to measure the parts of a whole—very rare): ut verba verbis quasi demensa et paria respondeant, Cic. Or. 12, 38; so Quint. 5, 10, 124 (al. dimensis): vos meministis quot calendis petere demensum cibum, i. e. the stated allowance of slaves, Plaut. Stich. 1, 2, 3.
Hence, dēmensum, i, n., a measured allowance, ration of slaves: quod ille unciatim de demenso suo comparsit, Ter. Ph. 1, 1, 9; Spart. Hadr. 7 fin.; Inscr. Orell. 2849; cf. Donat. ad Ter. l. l.; Sen. Ep. 80; Hor. Ep. 1, 14, 40 Orelli.
In a comic transf.: nunc argumentum vobis demensum dabo, Non modio neque trimodio, verum ipso horreo, Plaut. Men. prol. 14.